Engine system

The present disclosure relates to an engine system.

In related art, as for engines or the like installed in vehicles, discussions have been held about reducing a discharge amount of harmful substances, in other words, improving exhaust performance. For example, JP3000804B2 discloses an engine including a catalyst apparatus, the engine reducing an intake air amount in order to reduce a discharge amount of a harmful substance when a temperature of a catalyst apparatus is low and an exhaust gas purification capability by the catalyst apparatus is low.

As described above, because combustion gas generated in an engine body and thus an amount of exhaust gas can be suppressed when an intake air amount is decreased, a discharge amount of a harmful substance can be decreased.

However, in an engine which has an exhaust gas recirculation (EGR) passage in which a part of exhaust gas is returned to an intake passage, it is difficult to obtain sufficient exhaust performance when an outside air temperature is low solely by carrying out control to decrease the intake air amount when a temperature of a catalyst apparatus is low. Specifically, when the outside air temperature is low, water in the exhaust gas may freeze in the EGR passage. When freezing occurs in the EGR passage, a return amount of the exhaust gas, which is returned to the intake passage through the EGR passage, becomes insufficient, and as a result, the exhaust performance is likely to be degraded. As noted above, the engine of above JP3000804B2 has a problem in which under a condition where the temperature of the catalyst apparatus is similarly low, the exhaust performance is more likely to be degraded when the outside air temperature is low than when the outside air temperature is high, and there is room for improvement in this area.

The present disclosure has been made in consideration of the above-described circumstance, and an object thereof is to provide an engine system that can achieve proper exhaust performance.

For solving the above-described problems, the present disclosure includes: an engine body; an intake passage through which intake air entering the engine body flows; an exhaust passage through which exhaust gas exiting the engine body flows; an adjustment apparatus which adjusts an engine output parameter (such as engine torque or engine crankshaft rotation speed); an exhaust gas purification apparatus which is disposed in the exhaust passage and purifies exhaust gas; an EGR passage which connects the exhaust passage on a downstream side relative to the exhaust gas purification apparatus with the intake passage and returns EGR gas as part of exhaust gas to the intake passage; an EGR valve which opens and closes the EGR passage; an outside air temperature acquisition apparatus which acquires an outside air temperature; a purification apparatus temperature acquisition apparatus which acquires a purification apparatus temperature as a temperature of the exhaust gas purification apparatus; and a control apparatus which controls the adjustment apparatus and the EGR valve, and the present disclosure is such that the control apparatus carries out restriction control to control the adjustment apparatus such that an upper limit value of the engine output parameter (such as engine torque or engine crankshaft rotation speed) is set lower than a maximum value and the engine output or the engine torque has a value equal to or lower than the upper limit value in a case where the purification apparatus temperature is lower than a predetermined reference temperature, and sets the upper limit value to a lower value when the outside air temperature acquired by the outside air temperature acquisition apparatus is low than a value when the outside air temperature is high.

In the present disclosure, in a case where the temperature of the exhaust gas purification apparatus is lower than the predetermined reference temperature, the engine output or the engine torque is suppressed to the upper limit value, which is lower than the maximum value, or lower. This prevents a situation where a large amount of exhaust gas is generated in a state where a purification capability of the exhaust gas purification apparatus is low, and proper exhaust performance can be achieved.

Here, because a temperature of the exhaust gas flowing into the EGR passage is comparatively low in a configuration in which the EGR passage is connected to the downstream side relative to the exhaust gas purification apparatus, when the outside air temperature is low, water in the exhaust gas may freeze in the EGR passage. When freezing occurs in the EGR passage, a sufficient amount of exhaust gas (inactive gas) cannot be returned to the intake passage via the EGR passage, and degradation of exhaust performance, such as an increase in a discharge amount of NOfrom the engine body, is likely to occur. As noted above, even under the same condition where the temperature of the exhaust gas purification apparatus is lower than the reference temperature, the exhaust performance is more likely to be degraded when the outside air temperature is lower. To deal with this, in the present disclosure, when the restriction control is carried out in which the engine output or the engine torque is set to have the upper limit value or lower, the above upper limit value is set to a lower value when the outside air temperature is low than a value when that is high. Thus, while excessive lowering of the engine output or the engine torque is avoided by setting the above upper limit value to a higher value when the outside air temperature is high, discharge amounts of the generated exhaust gas and harmful substances such as NOwithin it can be suppressed to small amounts when the outside air temperature is low, and proper exhaust performance can be achieved.

In the above configuration, the control apparatus preferably prohibits opening of the EGR valve when the outside air temperature is lower than a predetermined reference temperature.

In this configuration, opening of the EGR valve is prohibited when the outside air temperature is lower than the reference temperature, and a flow of the exhaust gas in the EGR passage is stopped. Thus, water contained in the exhaust gas can be prevented from freezing in the EGR passage.

However, when the flow of the exhaust gas in the EGR passage and thus the return of the exhaust gas to the intake passage via the EGR passage are stopped, a discharge amount of NOfrom the engine body may increase excessively. To deal with this, in the present disclosure, as described above, because the above upper limit value is set to be a low value when the outside air temperature is low such as when the outside air temperature is lower than the reference temperature, an amount of the exhaust gas can be suppressed to a small amount. Thus, an increase in a NOdischarge amount can be suppressed.

In the above configuration, the engine system preferably further includes a high-pressure EGR passage which connects the exhaust passage on an upstream side relative to the exhaust gas purification apparatus with the intake passage; and a high-pressure EGR valve which opens and closes the high-pressure EGR passage. The restriction control is carried out as follows: when the outside air temperature is lower than a predetermined reference temperature, the control apparatus sets the upper limit value to a lower value than when the outside air temperature is equal to or higher than the reference temperature, and permits opening of the high-pressure EGR valve but prohibits opening of the EGR valve; when the outside air temperature is equal to or higher than the reference temperature, the control apparatus permits opening of both the EGR valve and the high-pressure EGR valve.

In this configuration, opening of the EGR valve is prohibited when the outside air temperature is lower than the reference temperature, and water contained in the exhaust gas can thereby be prevented from freezing in the EGR passage. Further, in this configuration, in a circumstance where opening of the EGR valve is prohibited because the outside air temperature is lower than the reference temperature, the above upper limit value is set to a low value, and return of the exhaust gas to the intake passage via the high-pressure EGR passage is permitted. Thus, whereas the prohibition of opening of the EGR valve may likely cause an increase in the NOdischarge amount, the NOdischarge amount can be suppressed by reducing the discharge amount of the exhaust gas and by introducing the exhaust gas via the high-pressure EGR passage.

In the above configuration, the control apparatus preferably sets a target EGR amount as a target value of an amount of exhaust gas to be returned to the intake passage, sets an upper limit amount of high-pressure EGR gas to be returned to the intake passage via the high-pressure EGR passage, and controls the high-pressure EGR valve such that the amount of high-pressure EGR gas has a value equal to or lower than the upper limit value. The restriction control is carried out as follows: when the outside air temperature is lower than the reference temperature and the target EGR amount is equal to or smaller than the high-pressure EGR gas upper limit amount, the control apparatus sets the upper limit value to the same value as when the outside air temperature is equal to or higher than the reference temperature; when the outside air temperature is lower than the reference temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, it sets the upper limit value to a lower value than when the outside air temperature is equal to or higher than the reference temperature.

In this configuration, in a case where the target EGR amount is realizable by return of the exhaust gas to the intake passage via the high-pressure EGR passage even when the outside air temperature is lower than the reference temperature, the above upper limit value is set to the same comparatively high value as the value when the outside air temperature is equal to or higher than the reference temperature. Thus, while the discharge amount of NOcan be suppressed to a small amount by realization of the target EGR amount, the engine output or the engine torque can be secured. Meanwhile, in a case where the outside air temperature is lower than the reference temperature and the target EGR amount is not realizable, the above upper limit value is set to a low value, and the discharge amount of the exhaust gas is reduced. Thus, in this case also, the NOdischarge amount can be prevented from excessively increasing.

In the above configuration, the engine system preferably includes an exhaust gas temperature detection apparatus which detects a temperature of exhaust gas, so that as the temperature of the exhaust gas, which is detected by the exhaust gas temperature detection apparatus, becomes higher, the control apparatus sets a lower value for the high-pressure EGR gas upper limit amount.

In this configuration, a situation in which a large amount of the exhaust gas passes through the high-pressure EGR passage in a high-temperature state is prevented. Thus, heat damage from the exhaust gas to peripheral components of the high-pressure EGR passage can be suppressed. Further, when heat damage is less likely to affect the peripheral components because the temperature of the exhaust gas is low, a return amount of the exhaust gas to the intake passage is secured, and the discharge amount of NOcan thereby certainly be reduced.

In the above configuration, the control apparatus preferably sets the upper limit value such that the upper limit value becomes lower as the purification apparatus temperature becomes lower when the outside air temperature is lower than the reference temperature and the target EGR amount is greater than the high-pressure EGR gas upper limit amount, such that the upper limit value becomes lower as a deficiency in the high-pressure EGR gas upper limit amount with respect to the target EGR amount becomes greater.

In this configuration, when the outside air temperature is lower than the reference temperature, the upper limit value can be set to an appropriate value which corresponds to the outside air temperature and the purification apparatus temperature.

As described above, an engine system of the present disclosure can enhance exhaust performance.

is an outline configuration diagram illustrating a preferable embodiment of an engine system of the present disclosure. An engine included in an engine systemillustrated inis a four-cycle diesel engine which is installed in a vehicle as a motive power source for travel. The engine includes an engine body, an intake passagethrough which intake air entering the engine bodyflows, an exhaust passagethrough which exhaust gas exhausted from the engine bodyflows, an HP-EGR apparatusand an LP-EGR apparatuswhich return a part of the exhaust gas flowing through the exhaust passageto the intake passage, and an exhaust turbocharging apparatuswhich supercharges the intake air flowing through the intake passage.

The engine bodyhas a plurality of cylinderswhich are aligned in a direction orthogonal to the page of(only one cylinder is illustrated in). The engine bodyincludes a cylinder block, a cylinder head, and a plurality of pistons. Each of the cylindersis formed with the cylinder blockand the cylinder head. That is, a plurality of cylindrical spaces which correspond to the plurality of cylindersare formed in an internal portion of the cylinder block, and the cylinder headis mounted on an upper surface of the cylinder blockso as to block the cylindrical spaces from an upper area. The pistonis housed in each of the cylindersto be capable of reciprocatively sliding.

A combustion chamber C is formed above the pistonof each of the cylinders. Each of the combustion chambers C is a space which is demarcated by a lower surface of the cylinder head, a side peripheral surface (cylinder liner) of the cylinder, and a crown surface of the piston. The combustion chamber C receives a supply of fuel injected from an injectorwhich will be described later. The pistonreceives combustion energy of the fuel supplied to the combustion chamber C and thereby performs reciprocating motion in an up-down direction.

A crankshaftas an output shaft of the engine bodyis provided below the pistonand in a lower portion of the cylinder block. The crankshaftis coupled with the pistonof each of the cylindersvia a connecting rodand rotates around a center axis in response to the reciprocating motion (up-down motion) of the piston.

A crank angle sensor SNand a water temperature sensor SNare mounted on the cylinder block. The crank angle sensor SNdetects a crank angle as a rotation angle of the crankshaftand an engine speed as a rotational speed of the crankshaft. The water temperature sensor SNdetects a temperature of cooling water which flows through internal portions of the cylinder blockand the cylinder head(in other words, an engine water temperature).

Fuel injectorsare mounted on the cylinder head. The fuel injectorsupplies fuel to the combustion chamber C of each of the cylinders. The fuel injectoris mounted on the cylinder headsuch that a distal end portion of the fuel injectoris exposed in the combustion chamber C. A plurality of injection holes as outlets of fuel are formed in the distal end portion of the fuel injector. The fuel injected from each of the injection holes is combusted by self-ignition in the combustion chamber C which is at a high temperature and a high pressure due to a compression action of the piston. In the engine according to the present embodiment, engine torque is changed mainly in accordance with an amount of fuel injected by the fuel injectors. As noted above, in the present embodiment, the fuel injectoris one example of an “adjustment apparatus” of the present disclosure. Note that in the following description and in, which will be described later, the fuel injectorwill simply be denoted as an injector. Other example components that can be used as the adjustment apparatus include a throttle valve, an intake valve operating mechanism, and/or an exhaust valve operating mechanism. It will be appreciated that each of these components can be used to adjust an engine output parameter, such as engine torque or engine crankshaft rotation speed. Further, the adjustment apparatus can include combinations of two or more of these components working together to adjust the engine output parameter.

In the cylinder head, intake portsand exhaust portsare formed. The intake portis a port which connects the combustion chamber C of each of the cylinderswith the intake passage. The exhaust portis a port which connects the combustion chamber C of each of the cylinderswith the exhaust passage. An intake valveis provided in the intake portof each of the cylinders, and an exhaust valveis provided in the exhaust portof each of the cylinders

The cylinder headis equipped with an intake valve operating mechanismand an exhaust valve operating mechanism. The intake valve operating mechanismdrives the intake valveof each of the cylindersto open and close in conjunction with rotations of the crankshaft. The exhaust valve operating mechanismdrives the exhaust valveof each of the cylindersto open and close in conjunction with rotations of the crankshaft. The intake valveperiodically opens and closes an opening of the intake porton the combustion chamber C side in response to driving of the intake valve operating mechanism. The exhaust valveperiodically opens and closes an opening of the exhaust porton the combustion chamber C side in response to driving of the exhaust valve operating mechanism.

The intake passageis a passage for introducing intake air into the combustion chamber C of each of the cylinders. The intake passagehas a surge tank in a portion, on a downstream side, which is close to the engine body. The surge tank is a tank which provides an expansion space for equalizing an amount of intake air into each of the cylinders. In a portion of the intake passageon an upstream side relative to the surge tank, an air cleaner, a throttle valve, and an intercoolerare sequentially provided. The air cleaneris a filter for removing foreign substances in the intake air. The intercooleris a heat exchanger which cools the intake air compressed by the exhaust turbocharging apparatus. The throttle valveis a valve which adjusts intake airflow. An air flow sensor SNis mounted on the intake passage. The air flow sensor SNis a sensor which detects the flow amount of the intake air, which enters the engine body, and is arranged in a portion of the intake passageon the downstream side relative to the air cleaner.

The exhaust passageis a passage for discharging the exhaust gas from the combustion chamber C of each of the cylindersout of the engine system. The exhaust passageis provided with a plurality of catalyststofor purifying various harmful components contained in the exhaust gas. Specifically, an oxidation catalyst apparatus, a Selective Catalytic Reduction Filter (SCRF), an SCR catalyst apparatus, and a slip catalyst apparatusare provided in this order from the upstream side (the side close to the engine body) of the exhaust passage. Further, a urea injectorand a mixing plateare provided in a portion between the oxidation catalyst apparatusand the SCRFin the exhaust passage.

The oxidation catalyst apparatushas a catalyst for oxidizing and detoxifying CO and HC in the exhaust gas (for converting into COand HO). The oxidation catalyst apparatushas a porous carrier and a catalyst substance such as platinum or palladium, which is carried by the carrier, for example.

The urea injectoris an injection valve which injects urea water made by dissolving high-purity urea into pure water. The urea injectorinjects the urea water, which is supplied from a urea water tank (not illustrated) installed in the vehicle, into an internal portion of the exhaust passage. Urea in the injected urea water is converted into ammonia (NH) by hydrolysis at a high temperature and is adsorbed on SCR catalysts included in the SCRFand the SCR catalyst apparatuson the downstream side.

The mixing plateis a plate-shaped member for stirring the exhaust gas flow. The mixing plateserves to uniformly disperse the urea in the urea water injected from the urea injectorand to send it downstream (to the SCRFand the SCR catalyst apparatus).

The SCRFis a filter with an SCR catalyst. The SCRFis an apparatus in which a catalyst substance such as platinum for combusting soot and the SCR catalyst are carried by a filter capable of collecting the soot in the exhaust gas. As described above, the SCRFadsorbs ammonia which is generated from the urea water injected by the urea injector. The SCR catalyst included in the SCRFis a selective reduction type NOcatalyst and reduces and detoxifies NOin the exhaust gas (converts that into Nand HO) by a chemical reaction using ammonia as a reducing agent. As the SCR catalyst, for example, vanadium, tungsten, zeolite or the like is used.

The SCR catalyst apparatusis an apparatus including the SCR catalyst and has a porous carrier and the SCR catalyst such as vanadium, tungsten, or zeolite which is carried by the carrier, for example. The SCR catalyst apparatusreduces NOwhich is not reduced by the SCRF. A casing is shared by the SCRFand the SCR catalyst apparatus, and the SCR catalyst apparatusis provided on an immediate downstream position of the SCRF. The above SCRFand SCR catalyst apparatuscorrespond to “exhaust gas purification apparatuses” of the present disclosure.

The slip catalyst apparatusis an apparatus which has an oxidation catalyst for oxidizing ammonia slipping from the SCRFand the SCR catalyst apparatus(in other words, the ammonia flowing out to the downstream side without being used for reduction of NO). As the slip catalyst apparatus, for example, an apparatus having a similar structure to the oxidation catalyst apparatuscan be used.

In a portion between the oxidation catalyst apparatusand the urea injectorin the exhaust passage, a NOsensor SNis provided which detects a concentration of NOin the exhaust gas. Further, in an immediate upstream portion of the SCRF(a portion between the mixing plateand the SCRF), an exhaust gas temperature sensor SNis provided which detects a temperature of the exhaust gas. The exhaust gas temperature sensor SNis one example of an “exhaust gas temperature detection apparatus” of the present disclosure.

The exhaust turbocharging apparatusis a supercharging apparatus which uses the exhaust gas exhausted from the combustion chamber C and thereby supercharges air to be supplied to the above combustion chamber C. The exhaust turbocharging apparatusincludes a compressorwhich is arranged in the intake passageand a turbinewhich is coaxially coupled with the compressorand is arranged in the exhaust passage. The compressoris arranged in a portion between the air cleanerand the intercoolerin the intake passage. The turbineis arranged in a portion of the exhaust passageon the upstream side relative to the oxidation catalyst apparatus.

The exhaust gas exhausted from the engine bodyenters the turbine, and the turbineis driven to rotate by the exhaust gas. The compressorrotates in conjunction with the turbineand pressure-feeds the intake air to the downstream side. In other words, the exhaust turbocharging apparatussupercharges to send the intake air in the intake passageto the engine bodywhile compressing the intake air.

The HP-EGR apparatusincludes an HP-EGR passageand an HP-EGR valve. The HP-EGR passageis a passage for returning the exhaust gas from the exhaust passageto the intake passage. The HP-EGR passageconnects a portion of the exhaust passageon the upstream side relative to the turbinewith a portion between the throttle valveand the compressorin the intake passage. The HP-EGR valveis a valve which adjusts a return amount of HP-EGR gas as the exhaust gas which is returned to the intake passagethrough the HP-EGR passage.

The LP-EGR apparatusincludes an LP-EGR passage, an EGR cooler, and an LP-EGR valve. The LP-EGR passageis a passage for returning the exhaust gas, which passes through the SCR catalyst apparatus, to the intake passage. The LP-EGR passageconnects a portion between the SCR catalyst apparatusand the slip catalyst apparatusin the exhaust passagewith a portion of the intake passageon the upstream side relative to the compressor. The EGR coolercools LP-EGR gas as the exhaust gas which is returned to the intake passagethrough the LP-EGR passage. The LP-EGR valveis a valve which adjusts a return amount of LP-EGR gas. In the following, the exhaust gas which is returned to the intake passageby the HP-EGR apparatusand the LP-EGR apparatuswill be referred to as EGR gas. In other words, the HP-EGR gas and the LP-EGR gas will collectively be referred to as EGR gas. Further, returning the exhaust gas by using the LP-EGR apparatuswill appropriately be referred to as LP-EGR, and returning the exhaust gas by using the HP-EGR apparatuswill appropriately be referred to as HP-EGR. Note that the LP-EGR passageis one example of an “EGR passage” of the present disclosure, and the LP-EGR valveis one example of an “EGR valve” of the present disclosure. Further, the HP-EGR passageis one example of a “high-pressure EGR passage” of the present disclosure, and the HP-EGR valveis one example of a “high-pressure EGR valve” of the present disclosure. Further, HP-EGR gas is one example of a “high-pressure EGR gas” of the present disclosure.

is a function block diagram illustrating a control system of the engine of the present embodiment. The engine systemhas a controller. The controlleris an apparatus for integrally controlling the engine and is configured with a microcomputer including a Central Processing Unit (CPU), Read-Only Memory (ROM), Random-Access Memory (RAM), and so forth. The controlleris one example of a “control apparatus” of the present disclosure.

Detection information by various sensors is input to the controller. Specifically, the controlleris electrically connected to the above-described crank angle sensor SN, water temperature sensor SN, air flow sensor SN, NOsensor SN, and exhaust gas temperature sensor SN, and various information detected by those sensors, for example, information such as the crank angle, the engine speed, the engine water temperature, an intake air flow amount, and the temperature of the exhaust gas is each and successively input to the controller.

Further, the vehicle is provided with an accelerator sensor SNwhich detects an opening (hereinafter referred to as an accelerator opening) of an accelerator pedal which is operated by a driver driving the vehicle, an outside air temperature sensor SNwhich detects an outside air temperature, and a vehicle speed sensor SNwhich detects a vehicle speed, and detection information by those accelerator sensor SN, outside air temperature sensor SN, and vehicle speed sensor SNis successively input to the controller. The outside air temperature sensor SNis an apparatus which acquires the outside air temperature by detection and is one example of an “outside air acquisition apparatus” of the present disclosure.

The controllercontrols each unit of the engine while executing various kinds of determinations, computation, and so forth based on input information from each of the above sensors (SNto SN). That is, the controlleris electrically connected to the injectors, the throttle valve, the urea injector, the HP-EGR valve, the LP-EGR valve, and so forth and respectively outputs signals for control to those devices based on results or the like of the above computation.

Control to be carried out by the controllerwill be described by using a flowchart in. Note that the flowchart illustrated inis repeatedly carried out every predetermined computation cycle while the engine is driven.

First, the controllercalculates an engine load, in other words, requested torque as engine torque which is requested by the driver of the vehicle (step S). The controllercalculates the requested torque based on the vehicle speed detected by the vehicle speed sensor SN, the accelerator opening detected by the accelerator sensor SN, and so forth. The requested torque is set to have a value equal to or lower than a maximum value of the engine torque that is a maximum value of torque realizable by the engine body. Note that the maximum value of the engine torque is set in advance based on a maximum combustion pressure, an air amount, and so forth.

Further, the controllercalculates a target value of an amount of the EGR gas to enter the cylinder, in other words, a target EGR amount as a target value of an amount of exhaust gas to be returned to the intake passage(step S). The controllersets the target EGR amount based on the requested torque, which is calculated in step S, and so forth. In the present embodiment, as the requested torque becomes higher, the target EGR amount is set to have a higher value.

Next, the controllerestimates an SCR catalyst temperature as a temperature of the SCRF(step S). The SCR catalyst temperature is one example of a “purification apparatus temperature” of the present disclosure.

In step S, the controllerestimates an input heat quantity to the SCRFand a dissipated heat quantity from the SCRFand estimates the SCR catalyst temperature based on those quantities. Specifically, the controllerestimates a flow amount of the exhaust gas based on the intake air flow amount, which is detected by the air flow sensor SNor the like, and calculates the input heat quantity to the SCRFbased on the flow amount of the exhaust gas and the temperature of the exhaust gas immediately in front of the SCRF, which is detected by the exhaust gas temperature sensor SN. Further, the controllercalculates the dissipated heat quantity from the SCRFbased on the vehicle speed detected by the vehicle speed sensor SNand the outside air temperature detected by the outside air temperature sensor SN. The controllercalculates the SCR catalyst temperature based on the calculated input heat quantity and dissipated heat quantity of the SCRFand a heat capacity of the SCRFwhich is stored in advance. The SCR catalyst temperature is calculated to be a higher value as the input heat quantity becomes larger or the dissipated heat quantity becomes smaller and is calculated to be a lower value as the input heat quantity becomes smaller or the dissipated heat quantity becomes larger. Here, the dissipated heat quantity from the SCRFcan be treated as a larger quantity as the vehicle speed becomes higher. This is because as the vehicle speed becomes higher, traveling air blowing against the SCRFincreases and causes more heat dissipation. Conversely, because the dissipated heat quantity becomes smaller as the vehicle speed becomes lower, the SCR catalyst temperature is estimated as higher as the vehicle speed becomes lower. As noted above, in the present embodiment, the SCR catalyst temperature is estimated by the controller, and the controlleris one example of a “purification apparatus temperature acquisition apparatus” of the present disclosure.